1. Field of the Invention
This invention relates to a monitoring system for monitoring the amount of light emitted from a surface emitting laser.
2. Description of the Related Art
There has been known a surface emitting laser which emits a laser beam in perpendicular direction to the active layer. Such a surface emitting laser is advantageous over an edge emitting semiconductor laser in that the angle of divergence of the emitted laser is substantially uniform in every direction in a cross-section of the beam and it is easy to form a laser array, and accordingly, there have been made various attempts of applying a surface emitting laser in various fields.
A semiconductor laser is generally driven under an automatic power control and accordingly it is necessary to monitor the amount of light emitted from the semiconductor laser. However since the surface emitting laser does not emit light rearward unlike the edge emitting semiconductor laser, the amount of light emitted therefrom cannot be monitored on the basis of the rearward emitted light.
In the case of the edge emitting laser, the amount of light emitted therefrom may be monitored by splitting a part of the forward emitted light by a beam splitter inserted into an optical system through which the forward emitted light travels and using the split part of the forward emitted light as a monitoring light. Such an arrangement of the light amount monitor may be applied to the surface emitting laser.
However, when a beam splitter is inserted into such an optical system, especially when a plurality of laser beams are used, the number of parts in the optical system increases, which adds to the size of the system in which the lasers are employed, and at the same time, positioning of the optical parts is complicated, which adds to the cost of the system.
When the surface emitting lasers are used as a laser array, a plurality of laser beams are emitted from the laser array, and accordingly increase in the size and cost of the system becomes serious.